Epoxy-based compositions are used frequently for encapsulation of microelectronic devices as well as for chip-and-board underfill processes, among others. Encapsulation is employed to protect components of electronic devices from environmental and thermomechanical stresses. Flip-chip technology employs underfill to reinforce solder joints by filling the space between the flip-chip die and the mounting substrate.
An encapsulant composition is applied to an electronic part to completely cover and protect the sensitive components such as the die, wire bonds, and capacitors. Encapsulants can be applied to the electronic devices by one of several methods including resin transfer molding, cavity filling dispense, dam and fill dispense, and stencil printing, resin film infusion, and liquid molding.
A “capillary underfill” process typically proceeds by first aligning the solder bumps on a flip-chip with the pads on a substrate, and the solder is reflowed to form the solder joints. After forming the solder joints, the underfill composition is flowed between the flip-chip and the mounting substrate. Thereafter, the underfill composition is cured. Capillary underfilling can be assisted by pumping the underfill composition between the flip-chip and the mounting substrate, or by vacuum-assisted drawing the underfill composition between the flip-chip and the mounting substrate.
The “no-flow” underfill process is another method of underfilling a flip-chip device. In a no-flow underfill process, the underfill composition is dispensed on the mounting substrate or the flip-chip, and the flip-chip and the mounting substrate are brought into contact. The solder bumps that are on the chip are aligned with the pads on the substrate. Next, the underfill composition is cured prior to or substantially simultaneously with reflowing the solder bumps to create the solder joints.
A die-attach material is used to connect a die to a heat sink, substrate, or another die. The die-attach material provides both adhesive and heat-transfer qualities between the die and the heat sink. Because of disparate materials between die, die-attach material, and heat sink, thermal stresses are present during heated operation of the die.